1. Field of the Invention
The present invention relates to a touch screen, and more particularly to an active touch screen and a driving circuit thereof.
2. Related Art
Touch is the most important sensory perception of human beings, and is the most natural way in human-machine interaction. The touch screen thus emerges and has already been widely applied in personal computers, smart phones, public information, intelligent household appliances, industrial control, and other fields. In the current touch field, the resistive touch screen, photoelectric touch screen, ultrasonic touch screen, and planar capacitive touch screen are mainly developed, and in recently years, the projected capacitive touch screen is developed rapidly.
So far, the resistive touch screen is still the mainstream product in the market. However, due to the double-layer substrate structure of the resistive touch screen, when the touch screen and the display panel are laminated in use, the reflection of the touch screen may greatly affect the display performance such as brightness, contrast, and chroma, thus greatly degrading the display quality, and the increase of the backlight brightness of the display panel may cause higher power consumption. The analog resistive touch screen has the problem of positioning drift, and needs calibration from time to time. In addition, the electrode contact working mode of the resistive touch screen also reduces the service life of the touch screen.
The display quality of the infrared touch screen and the ultrasonic touch screen is not affected. However, the cost of the infrared touch screen and the ultrasonic touch screen is high, and the water drop and dust may impair the working reliability of the touch screen. Particularly, due to their complicated structures and high power consumption, the infrared touch screen and the ultrasonic touch screen generally cannot be applied in portable products.
The planar capacitive touch screen has a single-layer substrate structure, and thus when the touch screen and the display panel are laminated in use, the touch screen only has a small impact on the display quality. However, the planar capacitive touch screen also has the problem of positioning drift, and needs calibration from time to time. The water drop may also impair the working reliability of the touch screen. Particularly, due to its high power consumption and cost, the planar capacitive touch screen generally cannot be applied in portable products.
The projected capacitive touch screen may also have a single-layer substrate structure, and thus when the touch screen and the display panel are laminated in use, the touch screen only has a small impact on the display quality. However, the projected capacitive touch screen detects the position of the finger or other touch objects on the touch screen by measuring the influence of the finger or other touch objects on the coupling capacitance between the electrodes of the touch screen, that is, by measuring the influence of the finger or other touch objects on the charging/discharging of the electrodes of the touch screen. The positioning point is obtained through analog computation, and thus the projected capacitive touch screen is not a real digital touch screen. The distributed capacitance in the manufacturing and use environment may affect the working reliability of the touch screen, and the interference of the display driving signal and other electrical signals may influence the working of the touch screen, and the water drop may also impair the working reliability of the touch screen. In addition, the projected capacitive touch screen has a high requirement for the resistance of the detecting line, such that the detecting line of the projected capacitive touch screen laminated with the display panel in use needs to have not only a low electrical conductivity transparent electrode layer like ITO, but also a high electrical conductivity electrode layer like metal. Therefore, the manufacturing process is complicated, and the cost is high, especially for the large-sized and even ultra large-sized touch screens.
As iPhone and Windows 7 operating system have been launched in recent years, people are more interested in multi-point touch. Since each sensing line on a screen, no matter on a resistive touch screen or a capacitive touch screen, is directly connected to multiple sensing units, sensing units are not completely independent of each other. In order to recognize multiple touch points, compared with single-point touch, the scanning mode of detection becomes more complicated and much time is spent on detection, or the judgment procedure after detection becomes complicated and requires strong computing power and large storage space and also consumes a lot of time. By improving the touch screen directly and modifying the detection mode accordingly, the sensing units on the screen can be completely independent and multi-point touch will become easy and natural.